Planar displays have great superiority in the portable display device and limited-space display market because they are lightweight and small. To date, in addition to liquid crystal displays (LCD), organic electro-luminescent displays (OLED), and plasma display panels (PDP), a mode of optical interference display is another option for planar displays.
U.S. Pat. No. 5,835,255 discloses an array of optical interference display cells of visible light that can be used as a planar display. Referring to FIG. 1, FIG. 1 illustrates a cross-sectional view of a conventional optical interference microelectromechanical display cell 108. Every optical interference display cell 108 comprises a cavity 110 formed therebetween a first electrode 102 and a second electrode 104 that are supported by supporters 106. The distance between the first electrode 102 and the second electrode 104, that is, the length of the cavity 110, is D. Either the first electrode 102 or the second electrode 104 is a semi-transmissible/semi-reflective layer with an absorption rate that partially absorbs visible light, and the other is a light reflective layer that is deformable when voltage is applied. When the incident light passes through the first electrode 102 or the second electrode 104 and into the cavity 110, in wavelengths (λ) of all visible light spectra of the incident light, only visible light with a wavelength λ1 corresponding to formula 1.1 can generate a constructive interference and can be emitted, that is,2D=Nλ  (1.1) where N is a natural number.
When the length D of the cavity 110 is equal to half of the wavelength multiplied by any natural number, a constructive interference is generated and a sharp light wave is emitted. In the meantime, if an observer follows the direction of the incident light, a reflected light with wavelength λ1 can be observed. Therefore, the optical interference display cell 100 is in the “open” status.
Referring to FIG. 2, FIG. 2 illustrates a cross-sectional view of the optical interference microelectromechanical display cell of FIG. 1 that is “closed”. The second electrode 104 is a deformable electrode that falls down while driven by the voltage. At this time, the length of the cavity 110 is changed. The reflected light after interference is either absorbed or becomes invisible light. An observer who follows the direction of the incident light cannot observe any reflected light in the visible light spectrum. Therefore, the display cell 108 is now “closed”. When the second electrode 104 falls down, an observer is supposed to observe a black display cell since, theoretically, the whole display cell is in the “closed” status. However, since the supporter 106 is transparent, incident light still can be reflected from the bottom surface 116 of the supporter. Furthermore, the cavity 110 in area 114 still has a considerable length allowing reflected visible light to emit therefrom since the second electrode 104 cannot stay close to the supporter 106. Therefore, even if the display cell 108 is in the “closed” status, the display cell 108 is not completely black since light still leaks from the bottom surface 116 of the supporter 106 and area 114.